Insulation Flaw Believed Cause of Titan Blast

The explosion of an unmanned Titan rocket above Vandenberg Air Force Base in April most likely was caused by the separation of insulation from the steel casing of a solid rocket booster, a government investigation disclosed Wednesday.

Because the cause of the accident was believed to be confined to one faulty rocket segment, rather than the result of a general design flaw, the Air Force expects to resume its satellite-launching program--brought to a standstill after a series of rocket failures in recent months--as early as the beginning of next year.

The head of the investigation said that the O-ring seals used by the Titan 34D--similar to those blamed for the Challenger space shuttle disaster last Jan. 28--did not play a role in the rocket’s April 18 accident.

“There is no relationship between this mishap and either the Challenger tragedy . . . or the August, 1985, loss of another Titan 34D,” said Air Force Brig. Gen. Nathan J. Lindsay, president of the board that investigated the accident. The earlier Titan accident was believed to have been caused by a fuel leak and a pump failure.

Since the space shuttle fleet was grounded after the Challenger disaster, such unmanned rockets as the Titan had been the nation’s only vehicles to launch satellites and other space payloads used for a wide array of communications and intelligence operations.

But after the Titan explosion 800 feet above Vandenberg, the loss of a smaller Delta rocket two weeks later at Kennedy Space Center, Fla., and the failure of a French Ariane rocket in May, Western nations lacked any means of launching satellites.

Before satellites can be launched again from Vandenberg, however, about $70 million in repairs must be made to electrical systems, fuel lines and the mechanical structure of the launch pad where the accident occurred, the Air Force said.

Timetable for Launch

“We’ll get back in the air, confidently, within the year, no question,” Lindsay said, later refining the timetable for the next launch to early in 1987. He refused to disclose the nature of the classified cargo that was aboard the rocket when it exploded or to discuss the backlog of satellites awaiting launch.

But John Pike, associate director for space policy of the Federation of American Scientists, said he believes they include “an early warning satellite and a pair of military communications satellites,” as well as a number of electronic eavesdropping orbiters.

Lindsay, a deputy commander of the Air Force Space Division in Los Angeles, directed an investigation team that included representatives of the Air Force, defense contractors, the National Transportation Safety Board and the National Aeronautics and Space Administration. They examined 30 to 40 possible causes and found no evidence of sabotage, he said.

“We believe the cause of the mishap was a failure in the thermal insulation in a segment of one of the two solid rocket motors,” he said at a Pentagon news conference. “The rubber insulation most likely separated from the steel rocket motor case, allowing damage by the propellant combustion products.”

Virtually Unexpected

This failure occurred on a booster five to seven inches below a joint between two of the motor’s six segments, Lindsay said. “It was a failure that we would have assigned a very, very low probability of ever occurring,” he said.

Although no signs of burning were found near the O-rings, where evidence of the shuttle failure was detected, NASA officials have been presented with the investigation’s finding, Lindsay said.

He said the insulation bonding technique employed in the shuttle’s solid rocket boosters, manufactured by Morton Thiokol Inc., is similar to that of the Titan, whose boosters are made by the Chemical Systems Division of United Technologies in Sunnyvale, Calif.

The loss of the Titan, the largest of the nation’s unmanned rockets, was particularly frustrating to the Air Force because similar rockets had been launched about 70 times and similar rocket motor segments had been fired 940 times--all without mishap.

Separation Mystery

In addition, he said, officials remained mystified by the cause of the separation of the insulation from the casing, which is made of steel three-eighths of an inch thick. They will attempt to find the answer by trying to duplicate the failure, Lindsay said, but he believes the reason the flaw escaped detection probably never will be found.

The general said sophisticated X-ray and ultrasonic techniques are used to examine the bond between the casing and the insulation, which keeps the intense heat and pressure of the fuel from burning through the rocket shell during liftoff. Those inspections will be increased and improved in future launches, he said.

Meanwhile, a NASA official said that the Delta failure on May 3 was probably the result of mechanical damage to wiring, and in Paris, a board of inquiry was said to have made 14 recommendations for resolving a problem of improper ignition of the Ariane propulsion system.